1. Field of the Invention
The present invention relates to a flashing controller, or more particularly, to a flashing controller for controlling a quantity of light by performing temporal control.
2. Description of the Related Art
With the development of an insulated gate bipolar transistor (hereafter, IGBT) or other device that is connected in series with a xenon flashtube of a strobe in a flashing apparatus and controls a flashing time merely by adjusting the gate voltage, a quantity of flashlight of a strobe in a flashing apparatus has come to be controlled temporally in recent years. The related arts have been proposed in conjunction with flashing controllers disclosed in Japanese Patent Laid-Open No. 2-298924 and U.S. Pat. No. 654818.
In the flashing controllers disclosed in the Japanese Patent Application Serial Laid-Open No. 2-298924 and U.S. Pat. No. 654,818, filed Feb. 13, 1991 and abandoned in favor of copending application Ser. No. 929,476, filed Aug. 17, 1992 a table defining the relationship between the Gv value specifying a quantity of strobe light required for optimal exposure and the flashing time is stored in the memory of a control circuit. Referencing the table, a flashing time of a strobe is retrieved according to a calculated Gv value permitting optimal exposure. The Gv value is a logarithm of a guide number (hereafter, G No) of a strobe and provided as the expression below. EQU Gv=Log.sub.2 G No.sup.2
FIG. 16 is a cross-sectional diagram of a flashing unit showing a flashing state of a conventional strobe. In FIG. 16, 51 denotes a reflector. 52 is a xenon flashtube. FIG. 17 shows a flashing circuit using an IGBT. In the flashing circuit, a charging circuit 54 driven by a power supply 53 loads a main capacitor 55 with a given electric charge, a flashing start signal from a flashing control circuit 56 is applied to a trigger electrode 57 to start flashing, then a flashing stop signal is applied to the IGBT 58 to stop flashing. Thus, an intended quantity of light is flashed.
However, even when the flashing time is controlled as mentioned above, a quantity of flashlight of a strobe may vary with the reflection state of the reflector 51 and depend on the characteristic of the xenon flashtube 52, the capacitance of the main capacitor, and the efficiency of the IGBT 58. To specify a quantity of light more reliably, the central values of the variations must be calculated. For this calculation, a tremendous amount of measured data is required. Furthermore, the characteristics of the above devices may not be established by a stage immediately before production. On the other hand, when a CPU employed for control circuits is mass-produced, programs must be completed about two months before the commencement of production. For the aforesaid prior art in which a flashing time is retrieved from a table listing quantities of light in association with flashing times, the table data may have been completed despite insufficient commitment to measurement and eventually incurred a serious designing risk. In particular, the shape of the reflector 51 tends to be determined at a late stage because it affects the appearance of a camera. This deprives the table of another necessary data.